Manufacture of artificial lumber and pressed and molded products



Man'ch 19, 136. F ARsm ZMBAM MANUFACTURE OF ARTIFICIAL LUMBER ANDPRESSED AND MOLDED PRODUCTS Filed Sept. 6, 1.932 2 Sheets-Sheet 1 rampCalifornia Redwood splinterysawdust m mixture Similar Material H at and9 Chemically Treat Screen through Add Coarse Screen. Hot mate m Top 9fMold 7 Screen Through 6 Fine Screen I Invert Mold and Contzants.

Mix Coarse Screened Particles with Part of Fluid Binder.

Add and Hix Fine Particles and Rest of Binder.

Screen Mixture 7 Into Cold. Mold.

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Patented Mar. 10, 1936 UNITED STATES PATENT OFFICE MANUFACTURE OFARTIFICIAL LUMBER AND PRESSED AND MOLDED PRODUCTS Application September6, 1932, Serial No. 631,919

4 Claims.

The present invention lies in a novel process of producing artificialfiat boards and shapes in any desired thickness and to any reasonabledimensions, and further lies in the production of a product greatlyimproving any and all comparable materials now commercially produced,

The invention will be described with the aid of the accompanyingdrawings in which:

Figs. 1 and 1a. are diagrammatic chain views jointly showing the varioussteps in the process.

Fig. 2 is a perspective view showing a small section of the product.

Fig. 3 is a fragmentary plan view showin part of one of the mold plates.

As my aggregate, I preferably select California redwood sawdust,preferably as now produced as wastage of the lumber industry, by thosesaws engaged in ripping with the grain of the wood rather than acrossthe grain, because the preferred sawdust is of the splintery varietyrather than the granular character of particles which are produced bycross-cut saws. In place of such sawdust however, I may use anyvegetable material placed by mechanical means in a splintery conditionresembling the sawdust described.

I prefer sawdust from wood dried to a point wherein it containsapproximately twelve percent of thenatural moisture of the tree, or asubsequent drying of the green sawdust to that percentage. Those skilledin the art will recognize that the moisture content of twelve per centmeans that the wood particles will at that point be completely dry tothe touch, yet retain the.

full measure of the strength of the wood, which would not be true werethe drying carried to a point below twelve per cent moisture content.

A characteristic of this wood, and also of many other vegetablematerials of like character, is that it contains a considerable quantityof water soluble tannates, lignins, and/or dye stuffs,

which through their uneven distribution, coupled sometimes with solublepitchy or adhesive substances, require a definite chemical treatment forthe purpose of neutralizing and rendering the same insoluble. I have,therefore, elected to so render inert the dye stuff, and the like andperforce must therefore destroy any natural resin, gum or adhesive, thiswood or other utilized vegetable substances may contain. The loss of thenatural adhesive content of the wood is of small moment, however,because very little pitch or resin exists in this material and whatlittle there is, is in isolated locations not evenly spread throughoutand would, therefore, if utilized, present a continuous problem ofvariables to a manufacturing process.

In that the time of addition of those materials to the sawdust whichwill neutralize natural adhesives, or render inert the soluble dyes andresins contained therein, and render them insoluble and infusible undertemperatures which I employ is a convenient moment for the performing ofother chemical results, I at this time add those materials whicheliminate the hygroscopic feature of this wood and render said woodhighly fire resistant. I may effect all of these results in thefollowing ways.

I place the sawdust in a closed mechanical mixer equipped for heatingand with vacuum and spray equipment, with the mixer in action, I heatthe sawdust to 200 F. and may spray (in a fog) a solution of water,acetic acid, di-ammonium phosphate and magnesium fluorosilicate, whichsolution has been heated to that same temperature.

My purpose is'to add the di-ammonium phosphate at a rate of 20 poundsper ton of sawdust; acetic acid at the rate of five pounds per ton ofsawdust, and magnesium fluorosilicate at the ratio. of ten pounds perton of sawdust (all weights approximate). To accomplish the same, I mustuse approximately one-hundred pounds of water per ton of sawdust, whichwater, after ten minutes mixing, I draw off by the coincidentapplication of the heat and vacuum in the usual way, leaving a moisturecontent in the sawdust at approximately the original twelve per cent setwhich will be set forth in detail in the followins:

The magnesium fluorosillcate is well known as a germ proofing andtermite proofing agent, as well as rot resisting agent.

I have above named acetic acid, di-ammonium phosphate and magnesiumfluorosilicate, but any weak acid or metallic salt, such as commercialalum or blue-stone, will serve, though in the case of a metallic salt,the solution containing that ingredient must be sprayed upon andabsorbed into the sawdust partic es before the application of thesolution containing the di-ammonium phosphate, because the interminglingof these two liquids would cause a chemical reaction which would defeatmy purpose.

I may introduce into the sawdust, in the mixer, a solution containingaluminum sulphate for the purpose of rendering insoluble the heretoforesoluble tannates, pectins, dye stuff and soluble lignins, etc., of saidwood particles. While this is my primary purpose the addition of thisaluminum sulphate under the influence of heat in the mixer andsubsequently heat and high pressure to which the mixture is in a laterstep subjected, likewise renders inert any pitchy or adhesive substancethe wood may contain, and through its widely known astringent action,cures the hygroscopic tendency of this wood. Further, the alum contentof the wood particles reacts with a later described binder which I sprayinto the mass, rendering the water soluble binder insoluble, partiallyso reacting when in the mixture and partially so reacting in thesubsequent operations.

I then add the solution containing the diammonium phosphate and themagnesium fluosilicate, sixty pounds of water containing the same; thisraises the moisture content to nineteen percent and the sawdust is stilldry to the touch. Notez-Sawdust, such as I have described, begins tofeel damp with approximately twenty-five percent moisture content.

In that the di-ammonium phosphate is held in this condition of drynessand fixed position in relation to the alum, it follows that the chemicalchange instant on contact in water solutions of the two, cannot takeplace in the sawdust except in a very minor degree negligible in myprocess.

As a later step, the addition of my glutinous, or viscous binder, takesup almost the entire capacity of the alum as a precipitant which will belater apparent.

It is possible to use sodium or potassium tungstate to replace thedi-ammonium phosphate with equal results. I can use the metallicchlorides with equal fire-proofing results.

In that I only use five pounds of alum per ton of sawdust, I need onlyforty pounds of hot water containing the same for the fine spray (fog),and in that the sawdust is dry (12% moisture content) this solution isimmediately absorbed integrally, only adding approximately 2% additionalmoisture, leaving said sawdust still in a condition of apparent dryness.

For my binding agent, I may use a solution of water soluble ureaformaldehyde condensation resin (gravity about 22 B at 65 F.) producedby the usual well known methods. I use this binder to a total of between10% and 30% of the entire mixture dependent upon the absorbent qualitiesof the sawdust, i. e. the absorbent qualities of sawdust from some logs(usually light weight second growth logs) being far greater than the Ikeep the two grades separate.

absorbent qualities of the butt logs from older growths.

The soluble urea formaldehyde resin on being tion, and upon subsequentlybeing subjected to high pressure and squeezed onto, and into, eachparticle of sawdust, forms an ideal binding medium which may, at thismoment, by continuation of the application of heat and pressure, beentirely converted to the completely insoluble and infusible state; or aproduct may be pro duced at this point containing a binder which isrigid when cold but pliable and plastic when heated, the above referredto rubbery state, through the fact that sufficient time under heat andpressure has not been given to render the binder completely infusible.In other words, the product may, at this point, be produced in athermo-plastic condition, or in a condition of rigid iniusibility andinsolubility.

I screen the chemically treated sawdust through a fourteen mesh screen,rejecting for regrinding all remaining on said screen. I then screen thescreened sawdust through a thirty mesh screen. I prefer to use sawdustof such graduation that approximately 75% lies between fourteen andthirty mesh and approximately 25% passes the thirty mesh, though this isonly for economizing in the use of binder, which is subsequently added,in that the fines are absorbent to a higher degree than the coarseparticles. Therefore, a larger percentage of fines will require a largerproportion or binder.

I introduce the coarser particles of screened sawdust into the abovedescribed mixer and mix cold five minutes with one-third of the binderrequired for the whole batch. I next introduce the fine material and theremainder of the binder and mix for fifteen minutes. The binder, in allcases, is sprayed into the mixture in as fine a spray (fog) as ispossible.

The preferable type of mixer is a rotary drum type equipped with bafflesto cascade the saw dust from the top to the bottom continuously as itrevolves to assure contact of all particles with the fog of bindersprayed therein as the mixer n revolves.

The purposes for which it may be necessary to produce the boardcontaining the binder in the rigid, infusible and insoluble conditionwill be further described.

For a binder, I can equally as well use the cresylic, phenol, glycol,tung, or vinyl resins, or the like resins, condensed with the aldehyde,or natural gums, or resins, or the like, in the same way as binders.Also the animal and vegetable glues are likewise adaptable to mypurpose. Also the cellulose, nitrates, acetates and xanthates arelikewise easily adaptable.

In place of a water soluble urea formaldehyde condensation resin as abinder, preferably with redwood sawdust as described, I can use for alike purpose any of the other binders named, or like materials, eventhough many of them are not water soluble. The binders named which arenot soluble in water can all be produced in liquid condition by the useof proper solvents. In solution of proper viscosity, each one may besprayed into and onto my treated vegetable particles and may be therebyadapted into my process without serious alteration in said process. Alsoeach water insoluble binder named in a solution of its proper solvent isemulsifiable with water, by the use of proper agents, and in thatcondition is adaptable directly into my process with my treatknown inthe art).

ed vegetable fibre, without'further serious change in my process.

If I use animal glue as a binder, I prefer to use such glue in theproportion of 7%, or less, in a water solution, and to add theretosodium bichromate or potassium bichromate to the quantity of 5% of theweight of dry glue contained. The bichromate of glue so producedondrying is harder than it would ordinarily be (a fact well This glue issensitive to sunlight (a fact also well known in the art). It is alsosensitive to the direct rays of the tungsten electric incandescent bulb,and to the action of heat, facts heretofore unknown in the art, insofaras I know. I, therefore, with the use of this material make my mixturein the presence of high candle power, tungsten electric light, tumblingand stirring the mix so as to activate the said bichromate of glue insuch way that upon the subsequent subjecting of the mat to heat,pressure, reheating and chilling, as my process outlined, the bichromateof glue becomes a water insoluble binder therein.

If I elect to use one of the water insoluble condensation resins, I doso by the use of emulsification. I proceed as follows, viz: I take analcohol solution of the cresylic acid and formaldehyde condensationresin, say grams of the same, in a viscous condition, comparable to theviscosity of the ordinary sodium silicate solution of commerce at 40' B.I heat the same to about F; and into the same I melt one gram of stearicacid. I heat separately 100 c. c. of water to 150 F'., adding theretoone gram of caustic soda. I mix the cresylic solution into the waterthereby producing a water thin emulsion in which the suspended particlesare so fine as to have all the appearance of a solution not changingcolor while hot, but solidifying to an opaque jelly when cold. Thisemulsion is sprayed hot into the mixture previously described(containing acid) and the emulsion subsequently breaks the resinprecipitating in a finely divided state on and in the particles of woodby reason of the acid action on the caustic soda portion of theemulsion, the resin thereby reconverting to the insoluble state.

The mass, on removal fro-m the mixer, is next run through a screen toassure freedom from lumps and/or uneven mixture. The mixture is stilldry to the touch, or at most only slightly moist.

The mixed material is next weighed out in direct ratio with the size ofthe product to be pressed, i. e., a board A, thick requiresapproximately 340 grams of mixture per square foot of surface, and thebatch is pressed in molds.

A novel feature of my process lies in the accomplishment of a uniformlayer of sawdust of uniform density in the mold before pressing thesame. The mixture is placed in a mold 5 equipped with a removable bottomplate 6, the contact surface of which has been oiled or waxed. Thisplate 6 is cold.

The accomplishment of a uniform layer of sawdust of the gradationspecified herein, of uniform density all-over its area was found to be amost diflicult task to achieve. Its accomplishment was absolutelynecessary because the product being pressed does not flow under heat andpressure, being of a fibrous character (splinters) and in no screenbeing equipped with square holes approxi mately each way, and screeningthe mixed sawdust therethrough into the mold. Upon the filling of themold 5 the sawdust piles up until it touches the bottom of said screenwhich is at a predetermined point, calculated to produce a predeterminedthickness of finished product. When the mold is filled, the screen 1 isremoved.

It was found that loosely piled sawdust, upon compression, produces asheet wherein one surface is more dense than the other and that the lackof uniform pressure shown thereby produces a sheet which subsequentlywarps.

The solution for this fault was found to lie in a preliminary compactionof the loose sawdust particles by vibrating from the top, for instanceby tampers 8. By this method of compacting, the sawdust compresses toapproximately onehalf the volume previously occupied and becomes apartly solid mass (splintery fibres intermeshed) without losing theprearranged uniform density over its area.

The fine material contained sifts away from the top surface leaving athin layer of the coarse splinters on that top surface.

As a further step in securing uniformity of appearance, texture, andgrain in the two sides of the finished product, and before subjectingthe same to pressure, it is necessary to install a waxed or oiled plate9 on the top, this plate being preheated to the temperature at whichpressure is to be applied. The wax or oil is applied to prohibitsticking or adhesion of the pressed product to the plate. The mold 5 isnow turned over thus reversing surfaces and what is now the top plate 6is removed. This plate, having been oiled, or waxed, on the contactsurface, upon removal takes with it, adhering to its surface, the layerof dust (material less than thirty mesh size) sifted onto it by thecompacting or tamping, leaving behind upon the surface of the formed butnot as yet compressed sheet, the coarse particles matted and interlacedin the same condition and of the same appearance as those coarseparticles previously described on the opposite side of said sheet. Thereason for this result, (removal of the dust with the plate 6) liesinthe fact that dust, hitting the waxed surface as the materials werescreened into the mold, adheres to said waxed surface instantly andinsulates said surface against adhesion of the larger particles. A newwaxed plate Ill heated is now installed on the top surface of the moldand the mat of sawdust is now readyfor compression under a hydraulicpress.

In that a usual size of product is approximately forty square feet inarea, it follows that molds with plates, etc., are of too great a weightfor economical handling by means other than mechanical. I, therefore,elect to have the molds installed upon a traveling surface and alloperations conducted as they slowly travel toward the press. That methodof operation, which I I believe originated in the automotive J beutilized for handling the molds.

industry, and is technically called "moving line production, is mypreferred method.

The metal plates used as contact surfaces with the sawdust beingconstantly heated and cooled, show a great tendency to warp. I havecured this fault by grooving the back of each plate as at 11 to /2 ofits thickness into a multiplicity of squares (see Fig. 3).

The press l2 may be of any desired vertical or horizontal form and ispreferably of a plural platen type, and suitable mechanical means mayThe sandwiches formed by the compact mats of splintery fibres and binderand the mold plates are compressed by this press at a pressure of about1250 pounds per square inch of cross-sectional area for approximatelyten minutes, at a temperature just under 100 C. My reason for holdingthe temperature under 100 C. is that the slight water content of themass (approximately 16% to by weight, including the water content of theurea formaldehyde resinous liquid binder) will not dissolve the lignoseor dye content of this wood due to the acidification thereof, previouslydescribed, but trapped steam caused uneven colors to appear upon thesurface of the final product, and in that temperature under the boilingpoint of water is sufiicient to accomplish my purpose, I use thistemperature which in itself prohibits the production of steam. I havelearned by practice that this method produces I a good uniform qualityof product from the press.

The press, molds, and material, are now cooled to room temperaturerequiring approximately three minutes, and the molds containing thepressed sheets are extracted from the press. The molds continue on themoving line (belt or roller conveyors) and the mold frame and top plateare removed and conveyed to a cleaning and waxing table, also heatingtables, then to the initial moving line for re-use. The pressed andcooled sheet is next removed from the bottom plate and continues forthfor further processing. The bottom plate follows the top plate.

The pressed sheet is next subjected to a coating of a substance which onfurther processing Waterproofs the sheet, adds strength and conveys suchcoloring for the finished product as may be desirable.

For this purpose, I may use the vinyl resins, such as are on the marketunder the trade-name of Vinylite. I use these materials in solutionbecause they are thermo-plastic when dry, soluble only in thearomatic-hydro-carbons and the like, and highly resistant to waterinfiltration, or to the action of caustic solutions or acid solutions,alcohols or oils, and are therefore ideal for ordinary commercial,industrial, or domestic utilization of the final product. Also they aremoderately inexpensive and easily procurable in commerce.

This resin, dissolved in proper solvents to a consistency of 25% to 50%resin content in, for example, toluol and/or benzole, can be applied bymeans of rolls or sprays l3 to the advancing, pressed sheet M in a coldcondition, and by the application of a warm dry air current t5, thehighly volatile solvents are removed, and the resin coating madeplastic; also, at this point, any free water contained within thepressed sheet is removed by evaporation. I use a resin with a softeningpoint, about 200 F. or less. While the resin remains plastic I pass thesheet through heated compression rolls l6 which press the resin into thewood surface of the sheet. 1'

next pass the sheet through cold rolls I! which chill the resin into thepores of said wood surface. The resin under my process is integral withthe surface of the sheet as it leaves the press, thereby forming anentire new surface which has a glossy finish and is impervious, as Ihave outlined, but which will take any paint finish.

By surfacing in this manner, I have produced a sheet useful in industryin its then existing condition, with great advantages over comparablesheet now commercially produced. My sheet is still in such conditionthat it can be pressed into any desirable shape when heated and if heatand pressure are applied in the usual way, i. e., two thousand poundsper square inch of surface, or less, at a temperature of approximately300 F. for approximately ten minutes, the urea formaldehyde resin binderof the wood particles will take on that insoluble, infusible cooked set,which assures permanent rigidity and provides that great resistance tothe passage of electricity so well recognized in that variety ofproducts now on the market, for that purpose. I refer to the ureaformaldehyde, cresylic acid formaldehyde, phenol formaldehyde, and thelike, condensation resins sold under various trade names such asBakelite, Redmonol, etc.

The sheet formed, pressed and surfaced as outlined, nowadvances to theautomatic trim saw which cuts it inpredetermined dimensions, trims ofiwastage, edge fins, etc. This saw is an ordinary article of industry andis not a concern of this patentapplication insofar as the details of itsconstruction or operation enter. The finished sheets are next stackedfor storage or for convenient shipment.

Instead of the vinyl resins in connection with the formation of myintegral surface, I can equally as well use any of the previously namedresins, the nitro-cellulose products, or the cellulose xanthateproducts, or the cellulose acetate products, or the like, for the samepurpose.

While I have limited myself to describing the production of sheets ofapproximate thickness, it will be apparent to all skilled in the artthat my process is adaptable to produce sheets of any reasonablethickness and can be utilized to produce dimension sizes and thicknessesof products. Said products can be produced, set, infusible, insolubleand sealed, as to surface, or can be produced strong and rigid atordinary temperatures, yet plastic, moldable, formable, and bendable,under the application of heat, and when subsequently cooled, will againtake on the condition of rigidity, retaining their surface sealing asheretofore described. Also in a condition wherein by the subsequentapplication of heat and pressure, the product may be pressed into avariety of forms and produce pavement, electrical insulation products,furniture parts, ornamental members and/or the like-set rigid,insoluble, infusible, highly fire resistant and impervious, as aboveoutlined.

Particular attention is invited to the chemical treatment of theaggregates; to the proportioning of the coarse and fine aggregates toobtain uniform mixture and maximum density of mix,

and uniform distribution of binder; to the screening of the treatedaggregate to assure uniform mix without lumps; to the manner of fillingthe molds to obtain a uniform layer of uniform density; to the vibratingfor securing maximum density before pressing to prevent warping of thefinal product; to the inversion of mold and removal of it coated topplate thereby removing the fine particles sticking to the coating tosecure uniform texture on both sides of the finished product; to theadvantageous binders and coatings used; to the adaptability of theprocess to produce a product hard when cold, and insoluble yetthermo-plastic for future molding or pressing, and capable of being atthat time set into rigidity, infusibility and insolubility, or which maybe produced in the first case set, rigid, infusible and insoluble.

I claim:

1. A method of preparing a molding composition which comprises treatingredwood sawdust produced in sawing redwood logs in the direction of thegrain and containing about 12 per cent moisture with an aqueous solutionof acetic acid, (ii-ammonium phosphate and magnesium fluorosilicatewhile the said sawdust is at a temperature of 200 F., screening thetreated sawdust through a fourteen mesh screen, screening the foregoingscreened sawdust through a thirty mesh screen, mixing a cresylic acidformaldehyde binder with the coarser of the above screened sawdust, thesaid binder being applied in the form of a fog which is sprayed onto thesawdust, adding the finer grade of the above screened sawdust, therelative proportion of the coarser and finer grades of sawdust beingapproximately three parts of coarser to one part of the finer sawdust,adding another portion of the said binder, and screening the abovemixture.

2. A, method of preparing a molding composition which comprises treatingredwood sawdust containing moisture but sensibly dry with an agentcapable of insolubilizing natural constituents of the sawdust, afire-retarding agent and a parasiticidal agent, screening the treatedsawdust to produce at least two grades of particle size, adding a binderof the class consisting of phenol formaldehyde condensation product,ureaformaldehyde condensation product, and a glue, to a coarser grade ofthe screened sawdust, admixing a finer grade of the screened sawdust,adding more of one of the above binders, thoroughly mixing the mass, andscreening the mixture.

3. A process of preparing a molding composition which comprisespreparing'sawdust by mixing coarser particles with a heat reactivebinder, adding finer particles and additional heat reactive binder,thoroughly mixing the mass, and screening the mixture.

4. A process of manufacturing board which comprises preparing a moldingcomposition from redwood sawdust by mixing coarser particles with a heatreactive binder, adding finer particles and additional heat reactivebinder, thoroughly mixing the mass, screening the mixture, introducingthe sawdust with admixed binder into a mold whose inner surfaces arecoated with an oily material, the said mold having a removable baseplate, tamping the mixture in the mold to homogenize the sawdust mixtureand inverting the mold, removing the base plate and inserting a new baseplate having an oily material on the inner surface thereof.

FRANCIS L. CARSON.

